“I’m proud to give Senator Isadore Hall my enthusiastic support," Hahn said in a statement provided first to CQ Roll Call. "As the incumbent State Senator and former Assemblyman for much of this district, Isadore has represented many of the communities within the 44th district for years."

Hall briefly ran for the seat in 2012 against Hahn and then-Rep. Laura Richardson but dropped out of the all-Democrat race before the primary. Hahn went on to handily defeat the scandal-plagued Richardson by a 20-point margin in the newly drawn district.

"Congresswoman Hahn is a close friend, a role model, and someone who I plan to work closely with both throughout this campaign and well beyond," Hall said in a statement to CQ Roll Call announcing his campaign. "I’m running for the 44th Congressional district seat to continue Congresswoman Hahn’s legacy of fighting for disadvantaged and middle class families, and to give a voice to those without one."

A handful of other Democrats could enter the race , including Los Angeles City Councilman Joe Buscaino, South Gate City Councilwoman Maria Davila and South Gate City Clerk Carmen Avalos.

But Hahn's early endorsement could potentially help clear the field in this heavily Democratic district, which includes the cities of Compton, Carson and the southern part of Los Angeles. President Barack Obama carried the majority-minority district by 71 points in 2012, making it one of the strongest Democratic districts in the country.

All candidates in California run on the same primary ballot. The two highest vote recipients move on to the general election, regardless of party identification.